1. Field of the Invention
The present invention relates to a rehabilitation system and method in which the position of the ankle is determined and force feedback is applied for the six-degrees of freedom of the ankle.
2. Related Art
Injuries to the lateral ligaments of the ankle are common injuries in sports and active life. The cause of ankle injuries is often insufficient strength and a lack of proprioception. Proprioception is a sense of joint position. Conventional rehabilitation exercises include strengthening the muscles that control position of the ankle and manipulating the ankle to teach the patient better awareness of joint position.
An ankle elastic band in a figure eight shape has conventionally been used for ankle rehabilitation. Patients place both feet through the holes of the band. When the patient moves their feet, the elastic supplies a resistive force to exercise the muscles that control the ankle.
Other conventional devices have been used for increasing strength and proprioception of the ankle. A pair of cylinder or half-cylinder foam rollers have been used to provide an unstable surface beneath the patient's feet. The patient balances on the roller to provide awareness of the ankle position. One example of such a device is a Biofoam Roller produced by Perform Better.
Another conventional device for increasing proprioception is a wobble board. Wobble boards are circular-shaped discs of wood or plastic with a hemispherical pivot in the center under the disc. Patients perform several exercises by putting either one foot or both feet on the board. By shifting their weight, patients can make the board tilt. Rehabilitation exercises include tilting the board from side to side or back to front and making the disc's edge touch the ground in a circular pattern. The exercises strengthen ankle muscles, improve balance and proprioception. An example is the wobble board produced by Kinetic Health Corporation.
U.S. Pat. No. 5,402,800 describes an ankle laxity measurement system in which a foot clamp is attached to a patient's foot. A reference point is established on the patient's tibia. Motion between the foot clamp and the reference point is measured in six degrees of freedom with six potentiometers or a transducer system. A separate device applies force to the foot clamp in inversion-eversion and anterior-posterior directions. Signals of the forces and six degree of freedom movement are interfaced to a computer to compute, record and display the measured motions and forces. The ankle laxity measurement can be used to diagnose a ligament injury and detect if there is an instability in the ankle once the ligament has healed.
U.S. Pat. No. 4,605,220 describes an ankle exerciser for strengthening healthy ankles and rehabilitating injured ankles. The exerciser includes a foot plate attached by a universal swivel joint to a support post. The foot plate can tilt or pivot about the longitudinal and transverse axes.
U.S. Pat. No. 5,413,543 describes a portable exercising apparatus. A lower stationary platform is attached to an upper mobile platform with a spring. The upper platform can move up and down or in a radial motion. A hand and forearm exercising strap is attached to the lower platform to allow pressure to be maintained on the foot.
Rehabilitation of body parts in a virtual environment has been described. U.S. Pat. No. 5,429,140, issued to one of the inventors of the present disclosure teaches applying force feedback to hand and other articulated joints in response to a user manipulating a virtual object. In addition, U.S. Pat. No. 5,577,981 discloses a computer controlled exercise machine providing virtual reality exercise regimens to the user. The positions of a user's feet are provided with two positioning sensing arrays of cables, spools and potentiometers. The arrays are attached to the lateral sides of the user's shoes to determine the length of stride and frequency.
It is desirable to provide an ankle rehabilitation system for providing position measurements and force feedback in six degrees of freedom of the ankle which system can include a virtual reality environment.